This invention relates generally to gas springs and more particularly to a sleeve type gas spring defining an annular gas pressure chamber.
Punch assemblies typically used in turret indexing presses have utilized a mechanical spring, such as a coil or belleville spring, to retract the punch after it has been driven or advanced by a mechanically or hydraulically actuated ram or some such other device. The mechanical spring used to retract the punch is subject to fatigue and wear in use and may break or otherwise fail in use and has a fixed spring rate or force which will retract the punch. Further, if a high force is desired to more rapidly or forcefully retract the punch, a larger mechanical spring is generally required which is undesirable in view of the compact configuration of the turret indexing press.
A sleeve-type gas spring for a turret indexing press has an annular piston operably associated with a punch tool to reciprocate therewith and defining in part an annular gas chamber constructed to receive a gas under pressure. As the punch tool and piston are driven to their extended position by a press ram or some other such power device, the volume of the gas chamber decreases thereby increasing the pressure within the gas chamber such that when the press ram is retracted, the pressure of the gas acting on the piston returns the piston and the punch tool to their retracted positions. The force acting to retract the piston and the punch is dependent on the pressure of the gas within the gas chamber and the change in volume of the gas chamber as the punch tool and piston are extended. Thus, the retracting force of the sleeve-type gas spring can be readily changed by varying the pressure of gas within the gas chamber to provide a spring which is versatile and which may be used with a plurality of different punch tools or in a plurality of different applications wherein varying retraction forces may be needed. Further, the sleeve-type gas spring has a very long life in service, can be easily recharged, and any worn seals easily replaced to facilitate servicing the gas spring.
Objects, features and advantages of this invention include providing a sleeve-type gas spring for use in a punch assembly such as a turret indexing press which can provide a force which is readily changeable to retract a punch or other work tool of the press, utilizes a readily available and inexpensive gas such as nitrogen to provide the force to retract the punch, can provide a relatively high force to retract the punch in a compact package, is of relatively simple design and economical manufacture and assembly, and has a long useful life in service.